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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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At least 325 records · Page 18
All sourcesNASA NTRSDOE OSTI
NASA NTRS1979

Transport properties of monatomic carbon. II - Contributions from excited electronic states

The aim of the present analysis is to verify the conventional assumption that the transport properties of atoms and molecules in excited electronic states are nearly the same as in the ground state. Reasonably exact calculations of the transport properties of excited-state carbon atoms are obtained on the basis of available experimental and theoretical data on the interactions between carbon atoms in excited electronic states. A comparison with results obtained with several models that have been used to estimate the transport properties of excited species indicates that the assumption under consideration is correct, but that the models do not predict very accurately the transport properties of excited species.

Biolsi, L.↗
NASA NTRS2006

Metallurgical Mechanisms Controlling Mechanical Properties of Aluminum Alloy 2219 Produced By Electron Beam Freeform Fabrication

The electron beam freeform fabrication (EBF3) layer-additive manufacturing process has been developed to directly fabricate complex geometry components. EBF3 introduces metal wire into a molten pool created on the surface of a substrate by a focused electron beam. Part geometry is achieved by translating the substrate with respect to the beam to build the part one layer at a time. Tensile properties have been demonstrated for electron beam deposited aluminum and titanium alloys that are comparable to wrought products, although the microstructures of the deposits exhibit features more typical of cast material. Understanding the metallurgical mechanisms controlling mechanical properties is essential to maximizing application of the EBF3 process. In the current study, mechanical properties and resulting microstructures were examined for aluminum alloy 2219 fabricated over a range of EBF3 process variables. Material performance was evaluated based on tensile properties and results were compared with properties of Al 2219 wrought products. Unique microstructures were observed within the deposited layers and at interlayer boundaries, which varied within the deposit height due to microstructural evolution associated with the complex thermal history experienced during subsequent layer deposition. Microstructures exhibited irregularly shaped grains, typically with interior dendritic structures, which were described based on overall grain size, morphology, distribution, and dendrite spacing, and were correlated with deposition parameters. Fracture features were compared with microstructural elements to define fracture paths and aid in definition of basic processing-microstructure-property correlations.

Domack, Marcia S.↗
NASA NTRS1972

Electron-beam-deposited thin polymer films - Electrical properties vs bombarding current.

Polymer films about 150 A thick, deposited on glass substrates by electron bombardment of tetramethyltetraphenyltrisiloxane, were studied, after being sandwiched between evaporated aluminum electrodes, the top one semitransparent. The capacitance, conductance, and photoconductance of the sandwiches were measured at room temperature as a function of the electron bombarding current which formed the polymer. The polymer thickness was obtained independently from Christy's (1960) empirical formula for the rate of formation. The obtained results indicate that, with increasing bombarding current, the polymer undergoes an increase in both crosslinking bonds and dangling bonds. Exposure to air drastically reduces the density of dangling bonds, but does not affect the crosslinking.

Babcock, L. E.↗
NASA NTRS1975

Pioneer 10 - Observations of energetic electrons in the Jovian magnetosphere

Data obtained by Pioneer 10 on the properties of energetic electrons in the Jovian magnetosphere are analyzed. The basic detectors (seven miniature Geiger-Mueller tubes) are described together with the signal processor and sampling techniques. The model of Jupiter used in the data analysis is a centered dipole with a tilt of 9.5 deg toward 230 deg System III longitude. The energetic-electron observations within the inner magnetosphere are found to indicate that radial as well as pitch-angle diffusion of energetic electrons must take place very rapidly. Outbound observations within the magnetodisk (the region beyond 20 Jupiter radii) are found to indicate a spiraling of the apparent location of the longitude of the dipole tilt, while inbound data indicate a constant value for the apparent longitude of the dipole tilt out to 70 Jupiter radii.

Randall, B. A.↗
NASA NTRS2001

Electron Beam-Cure Polymer Matrix Composites: Processing and Properties

Researchers from NASA and Oak Ridge National Laboratory are evaluating a series of electron beam curable composites for application in reusable launch vehicle airframe and propulsion systems. Objectives are to develop electron beam curable composites that are useful at cryogenic to elevated temperatures (-217 C to 200 C), validate key mechanical properties of these composites, and demonstrate cost-saving fabrication methods at the subcomponent level. Electron beam curing of polymer matrix composites is an enabling capability for production of aerospace structures in a non-autoclave process. Payoffs of this technology will be fabrication of composite structures at room temperature, reduced tooling cost and cure time, and improvements in component durability. This presentation covers the results of material property evaluations for electron beam-cured composites made with either unidirectional tape or woven fabric architectures. Resin systems have been evaluated for performance in ambient, cryogenic, and elevated temperature conditions. Results for electron beam composites and similar composites cured in conventional processes are reviewed for comparison. Fabrication demonstrations were also performed for electron beam-cured composite airframe and propulsion piping subcomponents. These parts have been built to validate manufacturing methods with electron beam composite materials, to evaluate electron beam curing processing parameters, and to demonstrate lightweight, low-cost tooling options.

Wrenn, G.↗
NASA NTRS2005

Pd/CeO2/SiC Chemical Sensors

The incorporation of nanostructured interfacial layers of CeO2 has been proposed to enhance the performances of Pd/SiC Schottky diodes used to sense hydrogen and hydrocarbons at high temperatures. If successful, this development could prove beneficial in numerous applications in which there are requirements to sense hydrogen and hydrocarbons at high temperatures: examples include monitoring of exhaust gases from engines and detecting fires. Sensitivity and thermal stability are major considerations affecting the development of high-temperature chemical sensors. In the case of a metal/SiC Schottky diode for a number of metals, the SiC becomes more chemically active in the presence of the thin metal film on the SiC surface at high temperature. This increase in chemical reactivity causes changes in chemical composition and structure of the metal/SiC interface. The practical effect of the changes is to alter the electronic and other properties of the device in such a manner as to degrade its performance as a chemical sensor. To delay or prevent these changes, it is necessary to limit operation to a temperature <450 C for these sensor structures. The present proposal to incorporate interfacial CeO2 films is based partly on the observation that nanostructured materials in general have potentially useful electrical properties, including an ability to enhance the transfer of electrons. In particular, nanostructured CeO2, that is CeO2 with nanosized grains, has shown promise for incorporation into hightemperature electronic devices. Nanostructured CeO2 films can be formed on SiC and have been shown to exhibit high thermal stability on SiC, characterized by the ability to withstand temperatures somewhat greater than 700 C for limited times. The exchanges of oxygen between CeO2 and SiC prevent the formation of carbon and other chemical species that are unfavorable for operation of a SiC-based Schottky diode as a chemical sensor. Consequently, it is anticipated that in a Pd/CeO2/SiC Schottky diode, the nanostructured interfacial CeO2 layer would contribute to thermal stability and, by contributing to transfer of electrons, would also contribute to sensitivity.

Lu, Weijie↗
NASA NTRS1991

All-electron molecular Dirac-Hartree-Fock calculations: Properties of the group IV monoxides GeO, SnO and PbO

Dirac-Hartree-Fock calculations have been carried out on the ground states of the group IV monoxides GeO, SnO and PbO. Geometries, dipole moments and infrared data are presented. For comparison, nonrelativistic, first-order perturbation and relativistic effective core potential calculations have also been carried out. Where appropriate the results are compared with the experimental data and previous calculations. Spin-orbit effects are of great importance for PbO, where first-order perturbation theory including only the mass-velocity and Darwin terms is inadequate to predict the relativistic corrections to the properties. The relativistic effective core potential results show a larger deviation from the all-electron values than for the hydrides, and confirm the conclusions drawn on the basis of the hydride calculations.

Dyall, Kenneth G.↗
NASA NTRS1993

All-electron molecular Dirac-Hartree-Fock calculations - Properties of the group IV monoxides GeO, SnO, and PbO

Dirac-Hartree-Fock calculations have been carried out on the ground states of the group IV monoxides GeO, SnO and PbO. Geometries, dipole moments and infrared data are presented. For comparison, nonrelativistic, first-order perturbation and relativistic effective core potential calculations have also been carried out. Where appropriate the results are compared with the experimental data and previous calculations. Spin-orbit effects are of great importance for PbO, where first-order perturbation theory including only the mass-velocity and Darwin terms is inadequate to predict the relativistic corrections to the properties. The relativistic effective core potential results show a larger deviation from the all-electron values than for the hydrides, and confirm the conclusions drawn on the basis of the hydride calculations.

Dyall, Kenneth G.↗
NASA NTRS1995

Simulated imaging properties of a series of magnetic electron lenses

The paraxial lens data were determined for a series of symmetrical magnetic lenses of equal lens diameter but variable air gap width for a wide range of lens excitations using the three-dimensional electrodynamic computer code MAFIA. The results are compared with a similar study done by Liebman and Grad wherein the field distributions within the lenses were measured experimentally with a resistance network analogue. Using these fields the lens data were obtained through numerical trajectory tracing. The utility of using MAFIA, instead of experimental methods for lens design is shown by the excellent agreement of the simulated results compared to experiment. Also demonstrated is the capability of using MAFIA to investigate aberration sources such as higher order off-axis magnetic field and space-charge effects.

Kory, Carol L.↗
NASA NTRS2014

Absolute Radiation Measurements in Earth and Mars Entry Conditions

This paper reports on the measurement of radiative heating for shock heated flows which simulate conditions for Mars and Earth entries. Radiation measurements are made in NASA Ames' Electric Arc Shock Tube at velocities from 3-15 km/s in mixtures of N2/O2 and CO2/N2/Ar. The technique and limitations of the measurement are summarized in some detail. The absolute measurements will be discussed in regards to spectral features, radiative magnitude and spatiotemporal trends. Via analysis of spectra it is possible to extract properties such as electron density, and rotational, vibrational and electronic temperatures. Relaxation behind the shock is analyzed to determine how these properties relax to equilibrium and are used to validate and refine kinetic models. It is found that, for some conditions, some of these values diverge from non-equilibrium indicating a lack of similarity between the shock tube and free flight conditions. Possible reasons for this are discussed.

Radiative Heating↗
NASA NTRS2022

Understanding the Properties, Wave Drivers, and Impacts of Electron Microburst Precipitation: Current Understanding and Critical Knowledge Gaps

Microbursts are impulsive (~100ms) injections of very energetic to relativistic electrons (energies from a few keV to MeV) into Earth’s atmosphere. Microbursts are important because they may represent a major loss process for the outer radiation belt (Ripoll et al., 2020). Understanding and quantifying the underlying causes and consequences plus relative importance of microburst precipitation represent outstanding questions in radiation belt physics and may have significant implications ranging from space weather to atmospheric chemistry. Chorus waves are the likely dominant cause of microburst precipitation, but important questions remain regarding the exact nature of the resonance generating the microbursts and the overall importance of the precipitation. These important questions are limited by lack of systematic coordination of simultaneous observations of causative waves in the magnetosphere and resulting precipitating particles at low altitudes. Increased funding for multi-spacecraft missions dedicated to answering these questions is critical.

Sadie Elliott↗
NASA NTRS2006

Electron Velocity Distribution Function in Magnetic Clouds in the Solar Wind

We present a study of the kinetic properties of the electron velocity distribution functions within magnetic clouds, since they are the dominant thermal component. The study is based on high time resolution data from the GSFC WIND/SWE electron spectrometer and the Berkeley 3DP electron plasma instruments. Recent studies on magnetic clouds have shown observational evidence of anti-correlation between the total electron density and electron temperature, which suggest a polytrope law P(sub e) = alpha(Nu(sub e) (sup gamma)) for electrons with the constant gamma approximates 0.5 < 1. This anti-correlation and small polytropic gamma-values is interpreted in the context of the presence of highly non-Maxwellian electron distributions (i.e. non-thermal) within magnetic clouds. These works suggested that the non-thermal electrons can contribute as much as 50% of the total electron pressure within magnetic clouds. We have revisited some of the magnetic cloud events previously studied and attempted to quantify the nature of the non-thermal electrons by modeling the electron velocity distribution function using a kappa distribution function to characterize the kinetic non-thermal effects. If non-thermal tail effects are the source for the anti-correlation between the moment electron temperature and density and if the kappa distribution is a reasonable representative model of non-thermal effects, then the electron velocity distribution within magnetic clouds should show indication for small K-values when gamma < 1.

Nieves-Chinchil, Teresa↗
NASA NTRS1978

Experiments on current-driven three-dimensional ion sound turbulence. I - Return-current limited electron beam injection. II - Wave dynamics

Pulsed electron beam injection into a weakly collisional magnetized background plasma is investigated experimentally; properties of the electron beam and background plasma, as well as the low-frequency instabilities and wave dynamics, are discussed. The current of the injected beam closes via a field-aligned return current of background electrons. Through study of the frequency and wavenumber distribution, together with the electron distribution function, the low-frequency instabilities associated with the pulsed injection are identified as ion acoustic waves driven unstable by the return current. The frequency cut-off of the instabilities predicted from renormalized plasma turbulence theory, has been verified experimentally.

Stenzel, R. L.↗
NASA NTRSDate not supplied

Connecting Uranus’ Magnetosphere and Upper Atmosphere via Electron Precipitation

Abstract. The precipitation of electrons is a key process through which significant energy is transferred from Uranus’ magnetosphere to its upper atmosphere. These electrons drive atmospheric ionization, thermospheric heating, and auroral emission at Uranus, and their properties are critical to address Uranus’ energy crisis as well as auroral phenomena. We combine measurements of auroral precipitation at Earth, Saturn, and Jupiter, with relevant Voyager 2 observations to estimate the properties of precipitating electrons at Uranus. In order to produce the measured aurora, energy fluxes of ~0.1mW/m 2 are required with energies of ~5keV.The acceleration of particles between the magnetosphere and thermosphere is predicted to be Earth-like, but with significantly lower overall energy flux and field aligned currents due to Uranus’ sparser magnetosphere. The height-integrated Joule heating rates of ~0.2 mW/m 2 are an order of magnitude lower than Earth

Daniel Gershman↗
NASA NTRS1997

Electron Affinity Calculations for Thioethers

Previous work indicated that polyphenyl thioethers possessed chemical properties, related to their electron affinities, which could allow them to function as vapor phase lubricants (VPL). Indeed, preliminary tribological tests revealed that the thioethers could function as vapor phase lubricants but not over a wide temperature and hertzian pressure range. Increasing the electron affinity of the thioethers may improve their VPL properties over this range. Adding a substituent group to the thioether will alter its electron affinity in many cases. Molecular orbital calculations were undertaken to determine the effect of five different substituent groups on the electron affinity of polyphenyl thioethers. It was found that the NO2, F, and I groups increased the thioethers electron affinity by the greatest amount. Future work will involve the addition of these groups to the thioethers followed by tribological testing to assess their VPL properties.

Sulton, Deley L.↗
NASA NTRS2009

Modeling the Strahl in the Solar Wind Using CLUSTER/PEACE Electron Distribution Functions

We present a study of kinetic properties of the strahl electron velocity distribution functions (VDF's) in the solar wind. These are used to investigate the pitch-angle scattering and stability of the population to interactions with electromagnetic (whistler) fluctuations. The study is based on high time resolution data from the Cluster/PEACE electron spectrometer. Our study focuses on the mechanisms that control and regulate the pitch-angle and stability of strahl electrons in the solar wind; mechanisms that are not yet well understood. Various parameters are investigated such as the strahl-electron density, temperature anisotropy, and electron heat-flux. The goal is to check whether the strahl electrons are constrained by some instability (e.g., the whistler instability), or are maintained by other types of processes. The electron heat-flux and temperature anisotropy are determined by modeling the 3D-VDFs to a spectral spherical harmonic model from which the moments are obtained directly from the spectral coefficients.

Vinas, Adolfo F.↗